This invention relates to single layer lift-off resist compositions which are improved in adhesion to substrates over prior art single layer lift-off resist compositions.
In prior art photoresist compositions for the single layer lift-off process, the effect of aromatic hydroxy compounds added as a dissolution accelerator enables to form a pattern shape having undercuts where the pattern contacts the substrate.
Because of the characteristic pattern shape, the prior art single layer lift-off photoresist composition has a reduced area of contact with the substrate. It is thus susceptible to pattern peel as compared with ordinary photoresist compositions. This becomes a substantial bar against the target of patterning to a smaller feature size.
An object of the invention is to provide a single layer lift-off resist composition which is improved in adhesion to a substrate and effective in preventing pattern peel.
The invention is directed at a positive-acting resist composition for use in the single layer lift-off process comprising a novolac resin and a quinonediazidosulfonate photosensitive agent. It has been found that when an aromatic hydroxy compound having at least one phenolic hydroxyl group in which the phenolic hydroxyl group is partially acylated, represented by the general formula (1) shown below, is used therein as a dissolution accelerator, the resist composition becomes more hydrophobic, forms a resist film firmly bondable to a substrate, and prevents from peeling.
Accordingly, the invention provides a single layer lift-off resist composition comprising a novolac resin, a quinonediazidosulfonate photosensitive agent, and an aromatic hydroxy compound having at least one phenolic hydroxyl group in which the phenolic hydroxyl group is partially acylated, represented by the following general formula (1). 
Herein m is an integer of 0 to 2, n is an integer of 0 to 2, with the proviso that m is 1 or 2 when n is 0. R1 to R6 are independently hydrogen, methyl, a group of the following formula (2), or a group of the following formula (3). When n is 0 and m is 1, A is hydrogen, methyl or a group of the following formula (2). When n is 0 and m is 2, one of A is methylene or a group of the following formula (4), and the other of A is hydrogen, methyl or a group of the following formula (2). When n is 1, A is methylene or a group of the following formula (4). When n is 2 and m is 1, A is methine or a group of the following formula (5). When n is 2 and m is 2, one of A is methylene or a group of the following formula (4), and the other of A is methine or a group of the following formula (5). At least one of R1 to R6 and A has a structure of a benzene ring having a hydroxyl group added thereto. 
Herein p, q, r and s are integers of 0 to 3, and t is an integer of 1 to 3.